Pedestrian and Bicycle Bridges and Tunnels

Pedestrian and bicycle bridges can range from short connections over streams
to extensive structures over freeways and major highways.

This underpass in Boulder, CO provides students with a route to school
that does not require crossing a busy street.

Pedestrian and bicycle bridges and tunnels are sometimes appropriate to improve
street or route connectivity or provide routes over or under roadways. Overpasses
and underpasses are most appropriate when children would otherwise be forced
to cross freeways or major multi-lane, high-speed arterial streets to travel
safely to or from school. There are also situations where pedestrian signals
are not warranted and/or feasible and overpasses and underpasses may be useful
during these times. Such separated crossings are most feasible where terrain
conditions allow for crossing over or under the roadway without having to provide
long ramps or steps. ADA guidelines require that all facilities be accessible
to all users, including those in wheelchairs and the visually impaired. Pedestrian
bridges and tunnels can be very costly to build. Bridges over an arterial street
will likely cost more than $1,500,000 and will often require extensive ramps.
The high cost of such grade separation should be considered along with security
issues, drainage problems, lighting needs and maintenance.

Pedestrian and bicycle bridges and tunnels can range from short connections
over streams to long bridges with extensive approach ramps over highways. The
location selected for any bridge or tunnel is an important factor in its effectiveness.
Like all pedestrian crossings, any facility that is inconvenient or requires
an indirect path will simply not be used. The effectiveness of a grade-separated
crossing depends on its perceived ease of use by the users. Pedestrians will
weigh the perceived safety benefit of using the bridge versus the extra effort
and time it will require when making a decision about where to cross. Often
it is best to redesign the crossing or modify the traffic control at the at-grade
crossing instead of building an over- or underpass. Some schools assign adult
school crossing guards at nearby bridges to assure that students use them.

Treatment: Pedestrian and Bicycle Bridges and Underpasses

Description/Purpose

Pedestrian and bicycle bridges and underpasses separate pedestrians and
bicyclists from vehicular traffic and allow for safe, uninterrupted pedestrian
and bicycle traffic flow. They are most appropriate for crossing a freeway
or other high-speed, high-volume arterial street or rail-line.

Expected Effectiveness

The effectiveness depends largely on the likelihood that they will be used
by pedestrians and bicyclists as an alternative to at-grade crossings. For
bridges and underpasses that are used by a large proportion of pedestrians
and bicyclists, studies have found that pedestrian-related crashes decreased
by 91 percent.[24] However,
other studies have determined that if the walking time to use an overpass
is 50 percent longer than crossing the street at-grade, then the bridge or
underpass will not be used and will be ineffective in reducing crashes.[25]

Evaluation Measures

Number or percent of pedestrian and bicycle crashes and changes in
probability of being involved in a crash once treatment is in use.

This guide was developed by the Pedestrian and Bicycle Information Center (PBIC) in collaboration with SRTS experts from around the country and support from the National Highway Traffic Safety Administration (NHTSA), Federal Highway Administration (FHWA), Centers for Disease Control and Prevention (CDC) and Institute of Transportation Engineers (ITE). View full list of contributors.